<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="js/jquery-3.5.1.js"></script>
</head>
<body>
<div style="background-color: lightpink">
    <form action="">
        <input type="date" id="birthdate" name="birthdate">
        <input type="checkbox" name="hobbies" value="eat">吃饭
        <input type="checkbox" name="hobbies" value="sleep">睡觉
        <input type="checkbox" name="hobbies" value="playIphone">玩苹果

    </form>
</div>

<script type="text/javascript">
    let e = $("input[name=hobbies]") ;
    e = $(":checkbox[name=hobbies]:first") ;
</script>
</body>
</html>